Brooding birds, presented with the choice between a smaller egg or a larger one, have been observed to choose the larger, even if it was artificial.
Birds presented with mealworms with secreted defences learned to avoid unpalatable prey on the basis of their colour signals more quickly than birds presented with mealworms with stored defences.
Of the birds presenting with clinical signs, 127 of a total of 153 (83%) sera were positive and of apparently healthy birds 6 of 40 (15%) samples were seropositive (Table 1).
Birds present dazzling ecological diversity, with species differing in their climatic requirements, the habitats they use for feeding and breeding and the food resources they consume (Del Hoyo et al., 1992-2010).
Wilhelm Kempff's 1950 recording of the First Legend ("St Francis of Assisi Preaching to the Birds") presents us with poetic Liszt playing of unsurpassed quality.
If some birds present in the survey unit are not detected with the intensive method, the population will be underestimated.
However, infection status was not associated with any other indices of immunity (all χ < 3.03 and all P > 0.22, except for IgY, which showed a marginal effect: χ = 5.61; P = 0.06 with PCR-positive birds presenting slightly lower IgY values than PCR-negative birds: mean = 0.61 ± 0.05 SE vs 0.72 ± 0.03).
Once birds consistently used the tool to retrieve food (8/10 on two consecutive blocks of 10 trials), the experienced birds were presented with tool-tubes containing training tools of four lengths (see above) within beak-reach, and a food-tube with food at different depths, out of beak-reach (food could be retrieved by 1 4 of the training tools, depending on food position).
They learned that A was always better than B, and C was always better than D. The confusion arose when the birds were presented with keys B and C together.
They spied on the females from behind a blind a few meters away as the birds were presented with multiple bachelors, some with big masks, some with bright yellow throats.
